1. Field of the Invention
The present invention relates generally to an information management system for providing information under management in response to a request, and more particularly to an information management system for managing state information on states of objects each variable in plural types of states, and providing the state information in response to the request.
2. Description of the Related Art
There has hitherto been known a system in which a server has hitherto managed pieces of information on the states of the objects (which will hereinafter referred to as [state information]), and the state information is provided in response to a request given from a client connected via a network. This system is classified into the following types.
(1) The server retains, as a set of information, plural pieces of state information on the state variations of the objects during a period from a certain point of time up to the present time (in a way that can segment the set of information). Each time the request is received from the client, the client is provided with all pieces of retained state information (First type).
(2) The server retains the state information on the state of the object at the present time as a latest piece of state information, and provides the client with only the latest state information in response to the client's request (Second type).
(3) The server retains, a latest set of state information, the plural pieces of state information on the state variations of the object during a period from a certain point of time to the present time, and also retains a copy of a single piece or plural pieces of state information that have already been provided to the client. When requested from the client, the server compares the latest state information with the copy of the state information, then extracts a different part of information therebetween, and provides the client with this different part of information as difference information (Third type).
There arise, however, the following problems inherent in the systems of the first through third types described above. Namely, according to the first type, the client is provided with all pieces of state information retained by the server. Hence, a quantity of the data transmitted to the client is larger than in the second and third types. Accordingly, a larger load is applied on the network than in the second and third types. Supposing that a transmission speed is the same, there increases a time for the client to obtain the state information from the server.
According to the second type, the server retains only the state information of the object at the present time. Therefore, if the client attempts to obtain all pieces of state information on the state variations of the object, the client must frequently requests the server to provide the state information. Accordingly, there might be a possibility in which the larger load is applied on the network than in the first and third types. Further, if the state variation of the object frequently occurs, even when the client again and again requests the server to provide the state information, the state information on the all the state variations can not be obtained in some cases.
According to the third type, the server retains the copy of the state information provided already to the client in order to create the difference information. Especially when a plurality of clients exist, the serve must retain the copy of the state information with respect to each client. Therefore, a capacity of resource (memory) for retaining the state information must be made larger than in the first and second types. Moreover, if the server manages the state information of the plurality of objects, the server must create and manage the copy of the state information with respect to each client, and hence a tremendous processing load is applied on the server.